Radiation monitoring system

ABSTRACT

A radiation monitoring system which continuously detects and measures low levels of radiation and radioactive materials in the surrounding atmosphere comprises a large volume multiple scintillation beta radiation detector with an alpha particulate radiation scintillation detector, and with background reduction being achieved by the use of an anti-coincidence cosmic ray and high energy photon shield. The use of coincidence and anticoincidence pulse techniques and passive logic circuitry reduce background and electronic noise. The beta radiation and alpha radiation detectors have their output connected to a ratio circuit to continuously generate an output signal indicative of the ratio of alpha radiation to beta radiation. The cosmic ray detector generates an inhibiting signal to block the output of the beta detector to prevent it from recording its response to naturally occurring cosmic radiation.

tlnited States Patent Battist [4 Oct. 23, 1973 RADIATION MONITORINGSYSTEM Filed:

Appl. No.: 80,572

Oct. 14, 1970 [57] ABSTRACT A radiation monitoring system whichcontinuously detects and measures low levels of radiation andradioactive materials in the surrounding atmosphere comprises a largevolume multiple scintillation beta radiation detector with an alphaparticulate radiation scintillation detector, and with backgroundreduction being achieved by the use of an anti-coincidence cos- [52]U.S. Cl. 250/715 R, 250/435 MR, 250/83.6 FT 51 Int. Cl. G0lt 1/20 mic yd hlgh energy Photon shleld- The use of [58] Field of Search 250/715 R,43.5 MR, incidence and anti-coincidence Pulse techniqlws and 250 T, FT,33 R passive logic circuitry reduce background and electronic noise. Thebeta radiation and alpha radiation 5 References Cited detectors havetheir output connected to a ratio cir- UNITED STATES PATENTS cuit tocontinuously generate an output signal indicative of the ratio of alpharadiation to beta radiation. 3,339,070 8/l967 Mam 250/7l.5 R The cosmicy detector generates an inhibiting Signal 3,336,477 8/l967 Sharp 250/715R bl k th t t f th b t d t t t t 3 388 254 6/1968 Haller et al. 250 715R 0 e e a 6 prfeven from recording Its response to naturally occurringcos- Primary ExaminerArchie R. Borchelt radlanon' AttorneyuaRobert Lalo9 Claims, 3 Drawing Figures F fv i; v's l 90 RM. SCINTILLATOR TUBE BLOCKl 7| 73 i VOLTAGE VOLTAGE i la SOURCE SOURCE l RM. SCINTILLATOR TUBEBLOCK I 92 e4 7/ I v I 46 42 44 RM. SCINT!LLATOR P.M. TUBE ROD TUBE 4omm? 3 5O VOLTAGE SOURCE SOURCE 48\ 53 PM. SCINTILLATOR LE TUBE R00 TUBE60\ /62 STORAGE AND 64 I l2 RECORDER um'r RATIO PRECIPITATING 24SCINTILLATOR VOLTAGE U E SOURCE, P M T B PATENIED m 2 3 191a 3.767.915SHEET F 2 I 7 v GG 5 I90 f so PM SCINTILLATOR I TUBE BLOCK 7| 73 iVOLTAGE vOLTAGE 18 O R E SOURCE I A 82 l t RM. SCINTILLATOR I 27 TUBEBLOCK i B3 46 42 44 PM. SCINTILLATOR P.M. TUBE ROD TUBE \/OLTZ 3 5OVOLTAGE SOURCE SOURCE 48\ I P.M. SCINTILLATOR A lol/ was t 5T 37 ssSTORAGE 64 AND 2 RECORDER UNIT RATIO PREClPlTAT|NG CIRCUIT 33 24SCINTILLATOR ,j'

A -3l VOLTAGE INVENTOR P.M.TUBE SOURCE/ LEWIS BATTIST RADIATIONMONITORING SYSTEM The present invention relates to a radiationmonitoring system, and it more particularly relates to a system forcontinuously monitoring alpha and beta radiation fromradioactivematerials in the surrounding atmosphere. i

' The maximum permissible concentration of radioactive materialspermitted to be released to the environment' from nuclear facilities,such as nuclear power plants, research establishments, nuclear fuelreprocessing plants, manufacturing plants, medical establishments andthe like, is currently regulated by federal law. Such undesirableradioactive materials include radioactive nuclides which decay by alphaand beta particle emission. For example, radionuclides decaying by theemission of alpha particles are biologically dangerous since they arebone seekers, and thus the concentration of such isotopes from nuclearfacilities are severely limited by law. In order to ascertain the levelof radioactive contaminants in the atmosphere surrounding a nuclearfacility, given quantities of air have been filtered near the facilityto determine the concentration of radioactive materials present inairborne particles in each given quantity of air. However, gaseousradioactive components are not detected by this method, and a continuousdirect measurement of the level of contamination is not possible.

Another technique, employed in nuclear. power plants, has been themeasuring of quantities of radioactive materials present in a portion ofthe effluent gases prior to discharging them to the environment. Thesequantities are then considered to be diluted by a given amount of airlocated within the immediate vicinity of the nuclear power plant.However, this method is not entirely satisfactory, since there is noassurance that a representative sample of the effluent gas and thecontaminants therein has been measured. Moreover, complete or adequatedilution of the contaminants upon release-:to the atmosphere ispresumed, but such a dilution does not always occur inpractice.

, In addition to the foregoing disadvantages of prior art radiationmeasuring techniques, the'presence of natu-f rally occurring radioactivematerials and fluctuations in amount therein adversely affect themeasurementsmade in accordance with prior art techniques. Therefore, itis desirable to be able to distinguish between natural radioactivematerials and artificially produced radioactive materials emanating fromnuclear facilities. In this regard, an increase in the level of activitycould be due to an increase in the concentration of natural ticulateradioactive materials in the surrounding atmosphere, and which takesinto account fluctuations of natural radioactivity due to changes inmeteorological conditions. Also, it would be desirable to have such asystem which contains a minimum number of moving parts and is designedfor efficient unattended operation for long periods, while requiringlittle or no maintenance.

Therefore, the principal object of the present invention is to provide anew and improved radiation monitoring system which directly andcontinuously measures the concentration of gaseous and particulateradioactive materials in the surrounding atmosphere, and which takesinto account fluctuations of natural radioactivity due to changes inmeteorological and other conditions.

Briefly, the aboveand further objects are realized in accordance withthe present invention by providing a system which includes an alpharadiation detector and a beta radiation detector which have theiroutputs connected to a ratio circuit. The ratio circuit generates aratio signal indicative of the ratio of the detected alpha radiation tothe detected beta radiation. With no change in the amount ofartificially produced radioactive materials present in the surroundingatmosphere,

7 fluctuations of natural radioactivity do not change the radioactivematerial and not due to any increase in the a concentration ofartificially produced radioactive materials. Naturally occurringradioactive components in the troposphere are ordinarily dominated byradioactive decay chains of the-inert gases radon and thoron which areproducts of natural radioactive decay in the uously measures theconcentration of gaseous and parratio circuit output which would remainconstant, since the ratio of the naturally-occurring alpha radiation tothe naturally occurring beta radiation remains constant. Thus, anychange in the output signal from the ratio detector indicates'a changein the level of artificial radiation in the surrounding atmosphere.Also,-

greater sensitivity in the detection of the low level activity isachieved by utilizing the ratio'circuit as compared to directlymeasuring and recording the numbers of alpha and beta particles.

' Inorde'rto prevent the, beta particle detector from responding tocosmic radiation or high-energy gamma radiation from radioactivematerials in the surrounding environment, a series of radiationdetectors are located above, and partially around the beta radiationdetector system. The signal obtained from the cosmic ray detector isused in anticoincidence with the signal from the beta detector, i.e.,there is provided a coincidence logic circuit which has its outputconnected to the ratio circuit and which responds to the output of thebeta detector and the absence of the output signal from a cosmic raydetector'which is disposed in a sealed chamber, whereby the coincidencecircuit inhibits the ratio circuit from responding to the beta detectordetecting cosmic radiation.

These and further objects of the presentinvention will be understoodmorefully and completely from the following detailed description whenconsidered with reference to the accompanying drawing,

FIG. '1 is a diagrammatic representation of a radiation monitoringsystem which'incorproates the principles of the present invention; I

FIG. 2 is an isometric view partially broken awa which depicts a housingembodying the apparatus shown in FIG. 1; and

FIG. 3 is apartially schematic view of an essentially conventional alphadetector,-and illustrates the blower or fan mounted in the housing forproviding a turbulent air flow past thealpha detector and into the betadetector.

Referring now to the drawing, the radiation monitoring system of thepresent invention generally includes an alpha radiation detector 12, abeta radiation detector 14, a ratio circuit 16 which responds to thealpha detector 12 and the beta detector 14 to generate a signalindicative of the ratio of detected alpha radiation to detected betaradiation, and a cosmic ray detector 18 which is disposed within asealed chamber 20 to prevent the detector 18 from responding to externalbeta radiation and which blocks the output of the beta radiationdetector 14 by inhibiting an electronic coincidence or logic AND gate 22which is interposed between the beta radiation detector 14 and the ratiocircuit 16. A storage and recorder unit 24 receives information from thealpha detector 12, the beta particle detector 14, the cosmic raydetector 18, and the ratio circuits 16 for storage and recordingpurposes. In operation, the alpha radiation detector 12 and the betaradiation detector 14 detect radiation and generate electrical signalswhich are recorded by the storage and recorder unit 24, and the ratiocircuit 16 generates an output electrical signal which is indicative ofthe ratio of the detected alpha radiation to the detected beta radiationfor storage and recording in the unit 24. This ratio remains constantduring fluctuations of natural radiation, but when the ratio signalgenerated by the ratio circuit 16 indicates that the ratio has changed,the change of the ratio is due to artificially produced and introducedradioactive materials in the surrounding atmosphere. The ratio circuit16 generates a ratio signal which can be either a digital-coded signalor an analog signal and which is indicative of the ratio of the numberof signals received from the alpha detector 12 to the number of signalsreceived from the beta detector 14 for a predetermined interval of time.In order to prevent the beta detector from erroneously responding to acosmic ray instead of beta radiation, the AND gate 22 responds to anoutput signal'from the beta detector 14 and the absence of an outputsignal from the cosmic ray detector 18. Thus, when the cosmic raydetector 18 detects cosmic radiation, the AND gate 22 is inhibited toprevent the beta detector 14 from generating an output signal inresponse to the cosmic radiation.

Considering now the system in greater detail, the alpha detector 12comprises a precipitating scintillator 25 which generates light pulseswhen particles'containing material which decays by emission of alpharadiation are attracted to and strikes the precipitating scintillator25, a photomultiplier tube 26 which detects the light pulses andconverts them into electrical output pulses, and a voltage source 28which drives the photomultiplier tube 26. The output of thephotomultiplier tube 26 is connected to one of the inputs of the ratiocircuit 16 via a conductor 31, and the output of the photomultipliertube 26 is also connected via a conductor 33 to the storage and recorderunit 24. The precipitating scincillator 25 is a lucite hemisphere whichis coated on its bottom side with a thin layer 113 of activitated zincsulphide. In order to make the layer electrically conducting, aconductor (not shown) in the form of a conductive inorganic reagent,such as magnesium perchlorate or in the form of a thin copper mesh, isimbedded in the zinc sulphide so that when the conductor is energized toabout minus two kilovolts, it attracts the particulates to the zincsulphide. Light pulses are emitted when the alpha radiation contacts thezinc sulphide of the precipitating scintillator 25. The photomultipliertube 26 may be any suitable photomultiplier tube, but an Amperex XP-lOOOphotomultiplier tube which is operated at 1500 volts potential, andwhich can be obtained from Amperex Electronic Corporation ofl-licksville, N.Y., is preferred. In order to distinguish a light pulsegenerated by alpha radiation contacting the zinc sulphide screen from apulse generated by the photomultiplier tube due to electronic noise,beta radiation activity, or a cosmic ray, the photomultiplier tube 26can be biased to detect only the larger signal produced in response toalpha radiation and to reject the other lower level signals.Alternatively, a limiter circuit (not shown) can be employed to mask theunwanted pulses in accordance with known techniques. In this regard,electronic noise is the source of the unwanted pulses and is generallycaused by dark currents" in the photomultiplier tube, noise pulsesproduced by an unstable power supply, or noisy circuit elements. itshould be understood that other types of alpha detectors, such as movingfilter belt systems, can be employed in place of the precipitatingscintillator 25 in accordance with the principles of the presentinvention.

The beta detector 14 generally comprises an array of scintillator rodassemblies shown illustrativelyin the drawing as 35 and 37, and a pairof voltage sources 39 and 40. The scintillator rod assemblies 35 and 37are identical to one another, and it is to be understood that only onescintillator rod assembly may be employed, or three or more scintillatorrod assemblies may also be employed in accordance with the principles ofthe present invention. The scintillator rod assembly 35 comprises aplastic scintillator rod 42 and a pair of photomultiplier tubes 44 and46 mounted on the opposite ends of the scintillator rod 42 to detectlight pulses generated by the scintillator rod 42 when it is acted uponby radiation. The scintillator rod 42 is a solid plastic rod composed ofplastic material, such as p-terphenyl plus ll, 4-4 beta phenylbutadienein polyvinyltoluene or polystyrene as the solvent. Such a solid plasticscintillator rod can also be purchased from Amperex ElectronicCorporation of Hicksville, New York and is designated as SPF fluorescentplastic scintillator". Rods which measured from k to 1% inches indiameter by approximately 8 inches long were successfully used, but itis to be understood that other sizes and shapes can also be used. Also,the number of rods is variable depending upon the sensitivity and volumeof air to be monitored. It should be understood that other types ofscintillator material, such as a plastic scintillator pipe having anoptically coupled polymerized clear methyl methacrylate core, a liquidscintillator material, or a sodium iodide solid rod which is thaliumactivated, can be used in place of a solid plastic rod scintillator, inaccordance with the present invention.

The photomultiplier tubes 44 and 46 detect light pulses produced by theplastic rod 42 when ionizing radiation interacts with the rod 42. Theoutputs 48 and 50 of the respective photomultiplier tubes 44 and 46 areconnected in parallel to the respective outputs 51 and 53 of thephotomultiplier tubes 55 and 57, respectively, of the scintillator rodassembly 37, and the outputs 48 and 51 are connected via a conductor 59to one of the inputs to the AND gate 22, the outputs 50 and 53 beingconnected via a conductor 60 to another one of the inputs to the ANDgate 22. Similarly, if additional scintillator rod assemblies areemployed, their outputs would be connected in parallel with the outputsIn operation, when a pair of photomultiplier tubes,

such as the photomultiplier tubes 44 and 46, detect a light pulse intheir scintillator rod, in the absence of an output signal from thecosmic ray detector 18, the AND gate 22 is energized to supply a signalto the storage and recorder unit 24 via a conductor 62 and to supply thesignal to the ratio circuit 16 via a conductor 64. By using a pair ofphotomultiplier tubes and by generating a signal in response to thecoincidence of the energization of the pair of photomultiplier tubes,electronic noise, such as dark currents in one of the photomultipliertubes, are not recorded. However, the natural background radiation isdetected, since it is desirable to record this type of information. As aresult, the apparatus ofv the present invention distinguishes betweenelectronic noise, and background radiation. Also, by utilizing a pair ofphotomultiplier tubes for each scintillator rod and by employing acoincidence circuit, further noise reduction is obtained. In thisregard, since the time constant of the flourescence of the scintillatorrod and the decay constant for the light pulse produced by the rod aresmall, in the order of nano-seconds, a high speed coincidence logic gatewhich has a switching time measured in nano-seconds can be employed byproviding a pair of photomultiplier tubes mounted on opposite-ends ofthe rod. By utilizing a separate voltage source, such as the voltagesource 39, for. each one of the photomultiplier tubes, such as thephotomultiplier tube 44, for a scintillator rod assembly any electronicnoise generated by the voltage source is not recorded, since the ANDgate 22 responds only to the coincidence of a pair of signals receivedfroma pair of photomultiplier tubes.

Considering now the cosmic ray detector 18, the detector 18 generallycomprises multiple array of scintillator block assemblies; 66 and 68 areillustrative of those employed, and a pair of voltage sources 71 and73.- The scintillator block assembly 66 is identical to the scintillatorblock assembly 68 and comprises a scintillator block 75 having a pair ofphotomultiplier tubes 77 and 79 mounted on opposite ends thereof fordetecting light pulses produced by the scintillator block 75 in responseto cosmic radiation. The scintillator blocks,

such as the scintillator block 75, are composed by plastic scintillatormaterial which is the same asthe material used in the scintillator rodsof the scintillator rod assemblies 35 and 37.

An output 80 of the photomultiplier tube 79 of the scintillator blockassembly 66 and an output 82 of the photomultiplier tube 84 of thescintillator block assembly 68 are connected in parallel and areconnected to one of the inputs of an AND gate 86 via a conductor 88.Similarily, an output 90 of the photomultiplier tube 77 is connected inparallel with an output 92 of a photomultiplier tube 94, and the twooutputs are connected to the other one of the inputs to the AND gate 86via a conductor 96. The output of the AND gate 86 is connected to thestorage and recorder unit 24 via a conductor 98 to record measurementsof cosmic radiation, and the output of the AND gate 86 is also connectedto the input to an inverter-logic gate 99 via a conductor 101, theoutput of the inverter gate 99 being connected to one of the inputs tothe AND gate 22.

As a result, when the cosmic ray detector 18 detects a cosmic radiationevent, the inverter gate 99 is energized to inhibit the AND gate 22,whereby if the cosmic radiation is detected erroneously by the betadetector 14, the event is not erroneously recorded by the storage andrecorder unit 24 as beta radiation. Thus, the cosmic ray detector 18serves as a shield for the beta detector 14 in lieu ofa cumbersome leadshield, which by necessity would be eight inches in thickness forattenuating a proton-electron cascade resulting from a shower ofnaturally occurring radiation from the surrounding atmosphere. 1

In a typical detection device incorporating the radiation monitoringsystem of the present invention, the alpha radiation detector and thebeta radiation detector preferably are mounted within an air chamber 104of a suitable housing 105 having an inlet 107 andan outlet 108 so thatan air moving device 110 such as a fan can continuously move the airfrom the inlet to the outlet at a known rate past both detectors wherebythe detectors can continuously measure the radiation in the air of thesurrounding atmosphere. In place of the air moving device, naturalcirculation may also be utilized. The cosmic ray detector is containedin a sealed chamber disposed abovethe .air chamber containing the alphaand beta detectors so as to shield the air chamber from an-air shower ofcosmic radiation from above. Alternatively, by employing a greaternumber of scintillator block assemblies, the sealed chamber containingthe cosmic ray detector can entirely or at least partially surround theair chamber. In this regard, it should be understood that a greater orlesser number of scintillator block assemblies can be employed by thecosmic ray detector, and if a greater number of scintillator blockassemblies are utilized, they would be connecte in parallel with theassemblies 66 and 68.

The photomultiplier tubes of each one of the scintillator blockassemblies are each energized by a separate voltage source so that noisesignals from the voltage source are not erroneously recorded by thestorage and recorder unit 24, since the AND gate 86 is only energized bythe coincidence of a pair of signals generated by both of thephotomultiplier tubes.

' While separate pairs of voltage sources are used for the alphadetector 12, the beta detector 14, and the cosmic ray detector 18, acommon pair of voltage sources can be employed for all three of thedetectors as long as two different voltage sources are used with thepair of photomultiplier tubes associated with a single scintillatorassembly.

Twelve scintillator rods arranged in a square array have beensuccessfully :used to monitor air containing concentrations of 10'microcuries per cubic centimeter of beta emitting radioactive materials.The spacing of the rods in the array depends upon the detectionefficiency for fission product beta emitting radionuclides. A separationof one foot between rod centers in a square configuration results in acontained volume of air, which volume is 9.4 cubic feet in an actualembodiment of the invention.

SUMMARY OF OPERATION A portion of the surrounding atmosphere is drawnvia a suitable intake tube 114 into the alpha precipitating scintillator25 assembly wherein particulates are elec' trostatically deposited onthe activated zinc sulphide layer 113 which is energized to about minus2 kilovolts as compared to the high voltage plate positive plate 120which underlies each precipitating scintillator assembly 25 in the alphadetector 12 and the alpha activity determined. The air and gases,radioactive and otherwise contained therein, are then introduced throughopening 121 into the beta detection chamber 122 containing the betascintillation detector. Preferably, a conventional diffuser plate isemployed which has openings which are spaced and sized and provided withguide vanes so as to assure uniform air flow through the chamber. Theair then passes through another diffuser plate into a plenum chamber 125from which it is exhausted to the outside environment through a suitableoutlet tube 108.

The beta detector array responds to gaseous components undergoingradioactive decay by emission of a beta particle or low energy photons.Operation of the cosmic ray shield 20, beta detector 14 and alphaprecipitating scintillator detector 12 and the interrelation thereofhave been described above. Thus, it is seen that the information fromeach detector and the cosmic ray shield are input to the storage andrecorder unit from which a conventional conductor assembly can be usedto transmit the signal to remote readout.

While the present invention has been described in connection with aparticular embodiment thereof, it will be understood that many changesand modifications of this invention may be made by those skilled in theart without departing from the true spirit thereof. Accordingly, theappended claims are intended to cover all such changes and modificationsas far as the true spirit of the present invention.

What is claimed is:

l. A radiation monitoring system for the continuous detection of gaseousradionuclides which are beta and low energy photon emitters present inthe surrounding atmosphere and for generating continuous signalsindicative of the amount of detected radiation for storage ortransmission comprising:

a housing including an air chamber having an inlet and an outlet analpha radiation detector mounted within said air chamber comprising anelectrostatic depositor capable of generating signals indicative of thedetection of alpha radiation from the decay of radon daughters,

a beta radiation detector mounted within said air chamber comprising atleast one scintillator body having a pair of photomultiplier tubesmounted on opposite ends thereof, capable of generating signalsindicative of the continuous detection of beta and low-energy photonemitting gaseous radionuclides in air flowing through said air chamber,-

a fan mounted in said housing adapted to continuously bring in outsideair and blow it from the inlet to the outlet of said air chamber pastboth said detectors, and

ratio means responsive to the signals from said alpha detector and alsoto the signals from said beta detector for continuously generating ratiosignals indicative of the ratio of the alpha indicating signals to thebeta and low energy photon indicating signals whereby the concentrationof gaseous radionuclides can be measured and man-made radiation in theair can be distinguished from naturually occurring background radiation.

2. A radiation monitoring system according to claim 1, further includinga cosmic ray detector for generating cosmic ray-indicating signalsindicative of the presence of cosmic rays, inhibiting means responsiveto said cosmic ray-indicating signals and to said betaindicating signalsfor inhibiting said beta-indicating signals upon the coincidence of oneof said cosmic rayindicating signals and one of said beta-indicatingsignals to prevent said ratio means from responding to thelast-mentioned beta-indicating signal, whereby said ratio means isprevented from responding to said beta detector detecting a cosmic ray.

3. A radiation monitoring system according to claim 2, wherein said betadetector includes a scintillation detector and a pair of photomultipliertubes operatively associated with said scintillation detector, saidtubes responding to light pulses produced by said scintillationdetector, and further including a pair of voltage sources individuallyconnected to said tubes for energizing them, and wherein said inhibitingmeans includes coincidence means responsive to the output of saidphotomultiplier tubes for generating said beta-indicating signals uponthe occurrence of the coincidence of said tubes responding to saidscintillation detector detecting beta radiation.

4. A radiation monitoring system according to claim 3, wherein saidalpha detector includes an activated zinc sulfide screen having anelectrically-energizable conductive means embedded in said screen toform a precipitating scintillator, and a photomultiplier tube responsiveto light pulses produced by said screen when said screen interacts withalpha radiation for generating said alpha-indicating signals.

5. A radiation monitoring system according to claim 2, wherein said betadetector further includes a plurality of scintillator assemblies havingpairs of outputs, corresponding ones of said pairs of outputs beingconnected together in parallel and to a corresponding one of a pair ofinputs to said blocking means, each one of said assemblies comprising ascintillation detector and a pair of photomultiplier tubes operativelyassociated with said scintillation detector forresponding to lightpulses produced by said scintillation detector to generate saidbeta-indicating signals.

6. A radiation monitoring system according to claim 3, wherein saidinhibiting means comprises said coincidence means and an inverter logicgate responsive to said cosmic ray-indicating signals for inhibitingsaid coincidence means.

7. A radiation monitoring system according to claim 3, further includinga cosmic ray detector coincidence means and a sealed chamber, whereinsaid cosmic ray detector is disposed within said sealed chamber and saidalpha detector and said beta detector or disposed outside of said sealedchamber, said cosmic ray detector including a plurality of cosmic rayscintillator assemblies having pairs of outputs, corresponding ones ofsaid pairs of outputs being connected together in parallel and to acorresponding one of a pair of inputs to the last-mentioned coincidencemeans, each of said cosmic ray assemblies comprising a cosmic rayscintillation detector and a pair of photomultiplier tubes operativelyassociated with said cosmic ray scintillation detector to generate saidcosmic ray-indicating signals.

8. A radiation monitoring system according to claim 7, wherein saidcosmic ray scintillation assembly comprising a cosmic ray scintillationdetector and a pair of photomultiplier tubes operatively associated withsaid tor to generate said cosmic ray-indicating signals.

9. A radiation monitoring system according to claim 8, wherein saidcosmic ray scintillation detector is comcosmic ray scintillationdetector for responding to light 5 prised of elongated solid Plasticmembers-

1. A radiation monitoring system for the continuous detection of gaseousradionuclides which are beta and low energy photon emitters present inthe surrounding atmosphere and for generating continuous signalsindicative of the amount of detected radiation for storage ortransmission comprising: a housing including an air chamber having aninlet and an outlet an alpha radiation detector mounted within said airchamber comprising an electrostatic depositor capable of generatingsignals indicative of the detection of alpha radiation from the decay ofradon daughters, a beta radiation detector mounted within said airchamber comprising at least one scintillator body having a pair ofphotomultiplier tubes mounted on opposite ends thereof, capable ofgenerating signals indicative of the continuous detection of beta andlow-energy photon emitting gaseous radionuclides in air flowing throughsaid air chamber, a fan mounted in said housing adapted to continuouslybring in outside air and blow it from the inlet to the outlet of saidair chamber past both said detectors, and ratio means responsive to thesignals from said alpha detector and also to the signals from said betadetector for continuously generating ratio signals indicative of theratio of the alpha indicating signals to the beta and low energy photonindicating signals whereby the concentration of gaseous radionuclidescan be measured and man-made radiation in the air can be distinguishedfrom naturally occurring background radiation.
 2. A radiation monitoringsystem according to claim 1, further including a cosmic ray detector forgenerating cosmic ray-indicating signals indicative of the presence ofcosmic rays, inhibiting means responsive to said cosmic ray-indicatingsignals and to said beta-indicating signals for inhibiting saidbeta-indicating signals upon the coincidence of one of said cosmicray-indicating signals and one of said beta-indicating signals toprevent said ratio means from responding to the last-mentionedbeta-indicating signal, whereby said ratio means is prevented fromresponding to said beta detector detecting a cosmic ray.
 3. A radiationmonitoring system according to claim 2, wherein said beta detectorincludes a scintillation detector and a pair of photomultiplier tubesoperatively associated with said scintillation detector, said tubesresponding to light pulses produced by said scintillation detector, andfurther including a pair of voltage sources individually connected tosaid tubes for energizing them, and wherein said inhibiting meansincludes coincidence means responsive to the output of saidphotomultiplier tubes for generating said beta-indicating signals uponthe occurrence of the coincidence of said tubes responding to saidscintillation detector detecting beta radiation.
 4. A radiationmonitoring system according to claim 3, wherein said alpha detectorincludes an activated zinc sulfide screen having anelectrically-energizable conductive means embedded in said screen toform a precipitating scintillator, and a photomultiplier tube responsiveto light pulses produced by said screen when said screen interacts withalpha radiation for generating said alpha-indicating signals.
 5. Aradiation monitoring system according to claim 2, wherein said betadetector further includes a plurality of scintillator assemblies havingpairs of outputs, corresponding ones of said pairs of outputs beingconnected together in parallel and to a corresponding one of a pair ofinputs to said blocking means, each one of said assemblies comprising ascintillation detector and a pair of photomultiplier tubes operativelyassociated with said scintillation detector for responding to lightpulses produced by said scintillation detector to generate saidbeta-indicating signals.
 6. A radiation monitoring system according toclaim 3, wherein said inhibiting means comprises said coincidence meansand an inverter logic gate responsive to said cosmic ray-indicatingsignals for inhibiting said coincidence means.
 7. A radiation monitoringsystem according to claim 3, further including a cosmic ray detectorcoincidence means and a sealed chamber, wherein said cosmic ray detectoris disposed within said sealed chamber and said alpha detector and saidbeta detector or disposed outside of said sealed chamber, said cosmicray detector including a plurality of cosmic ray scintillator assemblieshaving pairs of outputs, corresponding ones of said pairs of outputsbeing connected together in parallel and to a corresponding one of apair of inputs to the last-mentioned coincidence means, each of saidcosmic ray assemblies comprising a cosmic ray scintillation detector anda pair of photomultiplier tubes operatively associated with said cosmicray scintillation detector to generate said cosmic ray-indicatingsignals.
 8. A radiation monitoring system according to claim 7, whereinsaid cosmic ray scintillation assembly comprising a cosmic rayscintillation detector and a pair of photomultiplier tubes operativelyassociated with said cosmic ray scintillation detector for responding tolight pulses produced by said cosmic ray scintillation detector togenerate said cosmic ray-indicating signals.
 9. A radiation monitoringsystem according to claim 8, wherein said cosmic ray scintillationdetector is comprised of elongated solid plastic members.